A great deal of effort has been hitherto made to achieve high sensitivity of silver halide photographic light-sensitive materials. With regard to sensitizing dyes, it is considered that if the percent of light absorption is increased, the transmission efficiency of light energy to silver halide is improved and thereby high spectral sensitivity can be achieved.
However, the amount of the sensitizing dye adsorbed onto the surface of a silver halide grain is limited and adsorption of the sensitizing dye in excess of the single layer saturated adsorption is difficult to achieve. Accordingly, individual silver halide grains have a very low percent of absorption in terms of the quantum of incident light in the spectral sensitization region.
To solve these problems, the following methods have been proposed.
In P. B. Gilman, Jr. et al, Photographic Science and Engineering, Vol. 20, No. 3, page 97 (1976), a cation dye is adsorbed to the first layer and an anion dye is adsorbed to the second layer using the electrostatic force.
In U.S. Pat. No. 3,622,316, G. B. Bird et al describe a technique in which a plurality of dyes in multiple layers are adsorbed to silver halide and the Forster-type excitation energy transfer contributes to the sensitization.
In JP-A-63-138341 (the term "JP-A" as used herein means an "unexamined published Japanese patent publication") and JP-A-64-84244, Sugimoto et al describe a technique of performing the spectral sensitization by the energy transfer from a luminescent dye.
In R. Steiger et al, Photographic Science and Engineering, Vol. 27, No. 2, page 59 (1983), the spectral sensitization is performed by the energy transfer from a gelatin-substituted cyanine dye.
In JP-A-61-251842, Ikegawa et al describe a technique of performing the spectral sensitization by the energy transfer from a cyclodextrin-substituted dye.
With respect to the so-called link dye having two separate chromophores which are not conjugated but linked through a covalent bond, examples thereof are described in U.S. Pat. Nos. 2,393,351, 2,425,772, 2,518,732, 2,521,944 and 2,592,196 and European Patent 565,083. However, these are not used for the purpose of improving the percent of light absorption. In U.S. Pat. Nos. 3,622,317 and 3,976,493 which have an object of improving the percent of light absorption, G. B. Bird, A. L. Borror et al describe a technique of adsorbing a link type sensitizing dye molecule having a plurality of cyanine chromophores to a grain to thereby increase the percent of light absorption and effecting the sensitization by the contribution of the energy transfer. In JP-A-64-91134, Ukai, Okazaki and Sugimoto describe a technique of bonding at least one dye having substantially no adsorptivity and containing at least two sulfo groups and/or carboxyl groups to a spectral sensitizing dye capable of adsorbing to silver halide.
In U.S. Pat. No. 4,950,587, M. R. Roberts et al describe spectral sensitization by a cyanine dye polymer.
In this way, a large number of investigations have been made until now for improving the percent of light absorption, however, the effect of achieving high sensitivity is not yet satisfied and further, problems are present such as increase of the intrinsic desensitization and inhibition of the development.
Under these circumstances, a spectral sensitization technique of improving the percent of light absorption of a silver halide light-sensitive material and achieving high sensitivity is being demanded.